1. Field of the Invention
This invention relates to a viscosimeter for measuring the relative intrinsic or inherent viscosity of a solution in a solvent.
2. Description of the Related Art
According to the state of the art, the difference is made between the relative, the specific as, well as the inherent viscosity, and finally, the limiting viscosity number (intrinsic viscosity). By relative viscosity, we understand the quotient of the viscosity of the solution, for example of a polymer, to the viscosity of the pure solvent. The inherent viscosity results as the quotient of the natural logarithm of the relative viscosity divided by the concentration in gram of the dissolved substance per millimeter solution. There results herefrom the intrinsic viscosity as a limiting value of the inherent viscosity for the case that the aforesaid concentration goes towards zero. The so-called Hagen-Poiseuille""s formula is fundamental for viscosity measures. According to the state of the art, individual capillary measures are known for which the volume rate of the solution flow and the flow pressure drop are measured and, the geometric dimensions of the capillars being known, the viscosities of the examined liquids can be determined herefrom. The disadvantage of this measuring method consists in the unfavorable signal-to-noise ratio. The noise is essentially produced by high-frequency interfering signals of the pump which is required for conveying the substance to be examined. Moreover, irregular flow rates of the substance including the counterpressure fluctuations produce interfering signals on flow resistances. Finally, it is known that the viscosity is of course temperature-dependent, for which reason variations of temperatures during the measure can distort the measuring result.
According to the U.S. Pat. No. 3,808,877, to solve this problem, a flow limiter is used between the solvent feeding point and the measuring capillaries to produce a constant flow rate. The relative viscosity is determined by separate measures of the pressure drop on the capillary for the direct flowing polymer solutions and for the pure solvent. From this printed document, a device of two capillaries in parallel running legs is also known, one of them being filled with the polymer solution and the other one with the solvent. Basically, separated measures of said substances are also possible in such a way that the first substance flows through the first capillary and the second substance through the second capillary of a conduit during the measuring, whereby these capillaries are connected in series the one behind the other. The condition for carrying out an exact viscosity determination is in particular the geometric coincidence of the diameter and of the length of the used capillaries, likewise a temperature uniformity at the measuring points.
According to the EP 0 181 224, a capillary viscosimeter is proposed with two capillaries connected in series for which one serves as a reference capillary only for the solvent and the second as an analysis capillary for the polymer solvent solution. The capillaries consist of long thin tubes into which the solvent is introduced through a pump. A resistance path in the form of a tube with a small diameter is between the pump and the reference capillary which serves to produce a counterpressure. A further pulse attenuator can eventually be added to this resistance path. The differential pressure measured in the reference capillary (pressure drop) is supplied to a differential amplifier or to an evaluating unit just as the pressure drop which is measured on the analysis capillary. The feeding point for the substance to be examined, for example a polymer, is between the reference capillary and the analysis capillary so that the analysis capillary is traversed by a solution consisting of the polymer and the solvent. This arrangement connected in series can be changed as far as the feeding point for the test substrate can also be situated before the first capillary.
In this case, the first capillary becomes the analysis capillary. After having passed through it, the solution flows into a retaining vessel which assumes the function of diluting the solution further so that substantially only the solvent is measured by the reference capillary. In the described arrangement, a gel permeation chromatograph can be placed between the feeding point, for example for the polymer, and the analysis capillary, chromatograph in which polymer substances can be separated in a dilution solution according to their molecular size.
Besides the series connection described above, capillary bridge viscosimeters are also still known which are characterized by a relatively high sensitivity. In the bridge connection, a conduit is separated into two parallel running conduit parts in which there are respectively two capillaries connected in series. A place situated between the respectively first and the second capillary of each leg is connected with the corresponding place of the other leg over a connection conduit in which a high sensitive pressure sensor is placed.
According to the embodiment described in the EP 0 113 560, a retention basin in the form of a switchable bypass device is moreover provided for before the second capillary of a leg. As far as all existing four capillaries are flown through by the same liquidxe2x80x94and in particular without including the bypassxe2x80x94the connection conduit remains unpressurized. However, if a storage tank is placed above the bypass conduit, the second measuring capillary is substantially only flown through by the solvent so that there results a pressure drop with respect to the other measuring leg because of the different viscosities of the liquids. This pressure drop can be recorded and can be used for determining the viscosity.
Moreover, from EP 0 083 524, we still know devices with only one capillary which are supposed to have a length of several meters for a diameter between 0.2 and 0.3 mm. This capillary with a total length of, for example 3 mm, is wound in form of a loop with a diameter of at least 10 cm.
The aim of this invention is to improve the device mentioned in the introduction in order to avoid the detector dispersion appearing until now because of the used capillaries or to considerably reduce it and thus to increase the measuring accuracy of the device so that the least pressure differences are measurable.
According to an embodiment of the invention, a flow resistance with the smallest possible volume is used in the sample flow leg (hereunder designated as KV flow resistance), this flow resistance being placed directly behind the feeding point of the flow division. Accordingly, the viscosimeter shows flow resistances, such as disk-shaped or leaf-shaped Venturi nozzles or different KV flow resistances, with the smallest possible thickness and with a small volume with respect to all other parallel and following capillaries in a flow conduit system with two legs. This flow conduit system contains in the first leg at least three pressure reducing elements, for example capillaries, whereby behind the capillary following the branch point a pressure manometer is provided for with a connected bigger vessel, whereby behind further capillaries connected with each other with different diameters and with a big volume which corresponds to 100 to 1000 times the KV flow resistance in the second leg, a branch point leads to a differential pressure sensor or a sensor for differential pressure followed by capillaries with different diameters connected with each other up to the junction in a common outlet conduit. In the second leg, the KV flow resistance follows the branch point, this resistance being followed by further big volume conduits which lead to the branch point of the opposing side of the differential pressure sensor or of the sensor for differential pressure, whereby further capillaries connected with each other with different diameters and with different lengths follow the branch point, these capillaries joining into the common outlet conduit.
The viscosimeter comprises an inlet which runs into a junction from which the one capillary in one first leg leads over a big distance and with a comparatively big volume to a manometer (absolute pressure manometer) and from this to a still bigger vessel which has a 100 times to 1000 times bigger volume than the volume of the KV flow resistance in the second leg, a connecting conduit leading from the vessel to a pressure reducing element which is a capillary, a nozzle, a frit, or an appropriate supplying conduit which reduces the pressure in the flow conduit. The pressure reducing element is connected over a connection with a further capillary with a big volume which runs into the branch point, whereby the differential manometer or the sensor for differential pressure placed in the connecting conduit between the two branch points in both legs measures high sensitively the slightest pressure differences between the two branch points of the flow conduit. The big volume capillary following the connecting point leads over a connection to a further pressure reducing capillary, whereby the pressure reduction must not be identical with that in the upper section of the flow conduit. A connecting conduit follows the capillary into the junction of both legs to a common outlet conduit which makes possible the common discharge of the solvents from different flow lines. From the branch in the second leg, a pressure reducing element which can have different configurations leads directly into a big volume vessel and from there into a conduit with a big internal diameter which is connected by the branch with the differential manometer or differential pressure sensor, whereby the differential pressure sensor is switched here in such a way that it generates a positive signal for a pressure drop at the branch point, a conduit with a big internal diameter following the branch point, this conduit being connected over the connection with a pressure reducing capillary and constituting the access to the junction and to the outlet conduit.
The viscosimeter according to another embodiment also shows flow resistances, such as disk-shaped or leaf-shaped Venturi nozzles or different KV flow resistances with the smallest possible thickness and a small volume compared with all other parallel and following capillaries in a flow conduit system with two legs. Unlike the viscosimeter according to the first embodiment, the flow conduit system shows three parallel flow circuits among which at least two flow circuits are connected by a differential pressure sensor or sensor for differential pressure. These three flow circuits constitute an analogy to the Thomson bridge. The arrangement itself consists of an inlet which runs into a branch and divides into two legs, whereby one of the two legs comprises a pressure reducing element, a following branch point to a differential pressure and a pressure reducing element in the feeding conduit to a junction which runs into an outlet conduit. The other leg starting from the branch point comprises a pressure reducing element which leads to a branch which first leads into a big volume vessel leading to a junction and second which leads to a resistance capillary which is connected in the junction with the differential pressure sensor or the sensor for differential pressure and which is furthermore connected with a resistance capillary in the conduit led from the junction to a further junction, whereby the resistance capillary is connected on the outlet side over the junction with a pressure reducing element which runs over a conduit section into the junction and thus into the outlet conduit.
The invention according to another embodiment consists in that the viscosimeter shows flow resistances, such as disk-shaped or leaf-shaped Venturi nozzles or different KV flow resistances, with the smallest possible thickness and a small volume compared to all other parallel and following capillaries, whereby these flow resistances are placed directly behind the feeding points of the flow division and in the other partial leg behind the flow division there follows a long conduit with a big internal diameter which is furthermore more precisely defined by the fact that the capacity of this long tube amounts to 100 to 1000 times the KV flow resistance.
The KV flow resistance can be a very short capillary piece with a small internal diameter which is considerably lower than all other following or parallel running capillaries, a so-called microsystem technique component, for which engravings are built into the silicium basic material by photolytic methods and which can be connected in combination with external macroscopic flow resistances with viscosimeters according to the invention.
Furthermore, a KV flow resistance can also be created in that the flow resistances can be used for example in form of disk-shaped or leaf-shaped Venturi nozzle bodies with the smallest possible thickness. Here, the low spatial or volumetric dimension is decisive, which is advantageous in that, because of the favorable ratio of volume, the sample can be decomposed into nearly infinitesimal signal sizes in time and thus a systematic enlarging of the measuring signals through the measuring system, as it is observed for all measuring cells used according to the state of the art, is avoided. This enlarging had to be corrected, for example mathematically, up to now as far as this was possible. For example in the case of the Venturi nozzle body, the thickness should be smaller or bigger than 2 mm, preferably 2 mm or 3 mm. Preferably, the Venturi nozzle body flow opening is circular of slit-shaped. Alternatively, the nozzle body can however also have several hole-type openings of 1xcexc to 10xcexc. The channels of the microsystem technique components can have structures with a width of 10xcexc to 100xcexc. The same is valid for so-called fused silica capillaries and capillaries with which corresponding ratios of volume can be realized because of their internal diameter.
Basically, the KV flow resistance according to the invention can be used in all viscosimeters in which capillaries have been used until now. However, because of the high measuring accuracy which can be achieved, a bridge arrangement is chosen with two parallel running flow paths in which, among respectively three flow resistances placed the one behind the other, one KV flow resistance is at least respectively in one leg. Apart from that, the bridge arrangement known from the state of the art and described for example in the EP 0 113 560 can be gone back to.
Moreover, preferably a KV flow resistance, for example a Venturi nozzle or a microsystem technique channel is directly behind a gel permeation chromatography column, this being seen in flow direction, which is fundamentally known according to the state of the art with respect to its structure as well as to its mode of operation and which is already used for example in a viscosimeter arrangement according to EP 0 181 224.
With respect to Venturi nozzles existing one behind the other or in a branched bridge arrangement, a big volume retention basin can be provided for in the supply network for increasing the measuring speed. The function of these retention basins is basically known by the state of the art from the aforesaid printed documents, in series arrangements as well as in bridge arrangements.
For checking or for further detection, it can be advantageous to place a refraction detector or a membrane osmosis detector in the supply network. Further detectors are conceivable in specific combinations and represented in FIGS. 12 to 14.